1. Field of the Invention
The present invention relates to a buffer amplifier, and more particularly, to a buffer amplifier that has high input impedance and is less affected by temperature by supplying independent bias power to each of amplification units.
2. Description of the Related Art
In general, wireless communications systems include various wireless communication circuit blocks in order to perform operations such as amplification, filtering and frequency conversion on signals. Buffer amplifiers are used between various wireless communication circuit blocks to prevent a subsequent circuit block from electrically affecting a previous circuit block, prevent voltage drops which may occur when the input impedance of a subsequent circuit block is low, or prevent a fluctuation in the electrical characteristics of a previous circuit block due to external causes.
In general, the higher the input impedance and the lower the output impedance, the better buffer amplifiers are. Also, buffer amplifiers need to satisfy the characteristic of constant voltage gain as the occasion arises.
To realize the above characteristics, various types of related art buffer amplifiers have been developed. Representative examples of buffer amplifiers include source-follower type, differential type, and inverter type buffer amplifiers.
Source-follower type buffer amplifiers are widely utilized in wireless communication circuits because of their relatively high input impedance and low output impedance, but have limitations in that voltage gain is smaller than 0 dB all the time.
Differential type buffer amplifiers are robust against common noise and allow constant voltage gain, but use inductors or resistors as loads. In the case of using inductors, the differential type buffer amplifiers increase in volume and cause large voltage gain at a specific frequency. In the case of using resistors, differential type buffer amplifiers result in large current consumption and voltage drop, thus failing to increase output voltage, and have relatively high output impedance.
Inverter type buffer amplifiers have limitations concerning their high levels of operating input voltage, current consumption varying with conditions, and relatively high output impedance. To solve the limitations of inverter type buffer amplifiers, inverter type buffer amplifiers receiving a current source or DC bias have been developed. However, inverter type buffer amplifiers receiving the current source have relatively high output impedance and it is difficult to use them in low voltage processes. In inverter type buffer amplifiers receiving the DC voltage, voltage gain deteriorates rapidly depending on conditions involving process, voltage and temperature (hereinafter, referred to PVT conditions).